Reflectance Spectrophotometric Measurement of in vivo Local Oxygen Consumption in the Cerebral Cortex

A simple method was developed to measure in vivo local oxygen consumption quantitatively in the brain cortex. Reflectance spectra of tissue hemoglobin at the brain's surface were measured for assessment of both local tissue hemoglobin content and its oxygen saturation. Local oxygen consumption was calculated from the spectral changes of tissue hemoglobin during complete cessation of blood flow by compression of the cortical surface in the suprasylvian gyrus with the tip of an optic probe. This procedure was performed without any brain damage and only took ∼5 s. The calculated local oxygen consumption during this short period of compression remained constant for a few seconds. Then, it decreased rapidly, although the local tissue hemoglobin was not completely deoxygenated. The value of local cerebral oxygen consumption obtained by this method was 3.02 ± 0.61 mL O 2 /100 g brain/min; it was not influenced by the change in systemic blood pressure. The effect of pentobarbital on cerebral oxygen consumption was also studied. At the stage of burst and suppression on electrocorticogram, cerebral oxygen consumption decreased significantly (p < 0.001) to 1.03 ± 0.07 mL O 2 /100 g brain/min.